Molecular centrifugal process and apparatus



'Jan. 1, 1946. o. DENYS MOLECULAR CENTRIFUGAL PROCESS AND APPARATUSFiled Aug. 14, 1943 3 Sheets-Sheet 1 Jan. 1, 1946. O DENYS 2,392,124

MOLECULAR GENTRIFUGAL PROCESS AND APPARATUS Filed Aug. 14, 1943 5Sheets-She et 2 7 INVENTOR Jan. 1, 1946, 1 o. DENYS 2,392,124- MOLEC IJLAR CENTRIFUGAL PROCESS AND APPARATUS Filed Aug. 14, 1943 3Sheets-Sheath? $Y$TEM BEING EVA C'UA TED PRELIMINARY PUMP OR BA N DEN Y5INVENTOR ATTORNEY Patented Jan. 1, 1946 MOLECULAR CENTRIFUGAL PROCESSAND APPARATUS Orban Denys, Brooklyn, N. Y., assignor to DistillationProducts, Inc., Rochester, N. Y., a corpora tion of Delaware ApplicationAugust 14, 1943, Serial No. 498,693

6 Claims.

The invention is an improvement in molecular centrifugal apparatus. Ithas for its primary object the provision of a device for concentratingthe lighter molecules in a gaseous mixture of different molecularweights and the accessorial object of providing a more practical andsimpler rotary molecular vacuum pump.- The former being used inconjunction with the latter.

The term molecular weights as used herein, has to be interpreted in itsabsolute meaning, for instance, a substance composed of "n isotopes hasin my meaning n" weights.

The process of the primary invention, namely the molecular centrifugalgas concentrator, makes possible the concentration by mechanical meansof the gas of the lightest molecular weight in a gaseous mixture ofdiilerent molecular weights; this process if repeated a sufficientnumber of times will ultimately achieve the complete separation of thelightest gas from a gaseous mixture. This process is adaptable tovapors, thus making fractionation of a distiliand at very low pressurespossible. The process is further adaptable to the concentration andultimately to the separation of the isotopes of elements, and theircompounds which can be vaporized at a working temperature at very lowpressure.

In order to make these inventions more easily understood, a preliminaryillustration of the principles applied to both inventions is useful. Letus consider a horizontal passageof rectangular cross section containinga gas at such pressure that the mean free path of its molecules is largecompared to the transverse dimension of said passage and that one wallof said passage is moving in its own plane in a direction from left toright, then the molecules striking the moving wall will acquire avelocity having a tangential component equal to that of the moving walland a difference of pressure will be established between both ends ofthe passage; the high pressure side being at the right end of thepassage.

It can be deduced from the kinetic theory of gases that the abovementioned difierence of pressure is a function of the velocity of themoving wall and the molecular velocity of the gas, the latter in turnbeing a function of the molecular weight of the gas and its temperature;the lighter molecules at a given temperature having a greater .molecularvelocity than the heavier molecules at the same temperature. It isobvious that the molecules of a gas with a greater molecular.velocity-hence a gas with a smaller molecular weight-will strike themoving wall more often diiferent molecular than agas with a greatermolecular weight and consequently will have a tendency .of moving fasterin the direction of this wall than the heavier gas. 1

Still referring to the passage with its moving Wall, let us assume thatthe velocity of said wall can be regulated, that a vacuum pump isconnected at its left end while from the right end a gaseous mixture oftwo different molecular weights, due to the action of the pump, ismoving from right to 'left ata'con'stant velocity; moving the wall at arelatively slow velocity will slow down the flow of the mixture,increasing thisvelocity apprciably'might make the flow negative; betweenthese two velocitiesthere is an optimum velocity which has for'eifect toallow the heavier molecules, although their flow isretarded, to reachthe vacuum pumps inlet while the lighter molecules, striking more oftenagainst the wall are pushed back toward the passages inlet. Thus,according to this theory, we would have an accumulationof lightermolecules at the right end of the channel,- while the heavier moleculesare pumped out, It" is on'these principles that the primary invention,the molecular centrifugal gasconcentrator is based.

It will be apparent from these two illustrations that there is ananalogy between the two processes and their apparatuses, the one being amodification of the other. Both use a moving wall and as will beexplained further the one is not only accessorial but also complementalto the 7 other; they mutually contribute to produce a lar centrifugalvacuum pump which is used in conjunction with the molecular centrifugalgas concentrator, it shows the details of the lubricating system. i

v Figure 2 is an elevational view, partly insection, along the lines 2-2of Figure l; and

Figure 3 isa vertical section of a further modification; the molecularcentrifugal gas concentrator proper.

Fig. 4 is an elevation of. a complete apparatus showing the receptaclebeing evacuated by my improved molecular pump and the preliminarybacking pump.

Withreference to'Figures l and 2. it will be seen that the apparatuscomprises a cylindrical chamber having a diameter which greatly exceedsits height. This chamber is formed by two casings, which may bedesignated as a bearing: section 2 and a face-plate 3, fastened togetherby any suitable means such as the bolts 4 and nuts 5 Centered inface-plate 3, is a large opening 5 and a conduit 1 which serves as a gasor a vapor inlet. Bearing-section 2 has a smaller outlet I near theouter periphery of chamber I and a conduit 9 which serves to carry theflow from the chamber and can be connected to a preliminary vacuum pumpor condensation means .or both.

Centrally located on the outer face of bearing section 2 is a projectionI which in turn carries a pair of lugs II by which the apparatus may bemounted to any suitable support, which not forming part of the presentinvention is not shown. Projection III, in turn, is centrally pierced bythe bore |2 which serves as a bearing for shaft l4. On the outerextremity of shaft I4 is mounted a driving pulley I5 which is fastenedto the shaft by any suitable means and is spaced from the extreme end ofthe projection III, by means of the ballbearing l6.

Inside chamber on the other end of shaft I4 and mounted for rotationwithin chamber I is a large disk l8. This disk is made of such a formthat the stress at any point between the center and the rim is constant.Its profile is concavm convex. It is called a disk of uniform strength.As further illustration it can be said that this disk is so designedthat when rotating at its operating speed its strength at any point issafely sufficient to overcome the? centrifugal stresses at itsperiphery; in other words it is the theoretical lightest disk that canbe practically and safely rotated at a given speed. The diameter of diskI! is such as to provide a substantial clearance l9 between itsperipheral edge and the inner wall of chamber Disk It, in Figure 1 isshown as made integral with the shaft l4. However, it may be separatelymade and fastened to the shaft in any adequate manner. It is to be notedthat a hole in the disk will considerably weaken it unless its crosssection is greatly enlarged toward its center and this complicatesunnecessarily the design of the disk.

Figure 1 also shows the connection for the lubricating system. The bore|2 in bearing-sec- 22 are provided, also to serve as oil wells. Opposinghelical grooved passages 23 and 23 in the body of the bearing sectionserve to" connect the central well with the end wells 2| and 22respectively.

Three, aligned, small conduits 24, and 2S serve to connect oil wells 20,2| and 22 respectively with an oil reservoir 21. The internal d1.-arneter of these conduits is such as to insure an appropriate rate offlow of oil; they can furthermore be provided advantageously withsuitable fiow regulating devices. These conduits also serve as a supportfor the reservoir. Shaft I4 is very carefully fitted to the bearingsurfaces of bore |2, allowing the least possible practical tolerance.Rotation of shaft H in bore |2 causes oil to move from wells 2| and 22to the center well 20, up through conduit 24 to reservoir 21 and thenceback through conduits 25 and 26 to the wells 2| and 22. The purpose ofthis lubricating device is three fold. First it provides a continuouslycooled lubricant to the bearing and its shaft, it also insures againstthe oil being forced past its bearing and it also is a vacuum seal.Preferably, helical grooves 23 and 23 extend somewhat beyond theopenings 2| and 22 in order to insure proper operation. Makeup oil, toreplenish losses during operation, may be added through an openingnormally closed by cap 3|, in the top of reservoir 21. This cap can alsobe advantageously replaced with evacuating means which have for thepurpose to evacuate gases slowly dissolving in the oil.

With reference to the modification shown in Figure 3, it will be seenthat the apparatus like that in Figures 1 and 2, comprises an enclosedcylindrical chamber made up of a face-plate 4| and a bearing-casing 42.Faceplate 4| has a large central opening 52'. Bearing casing 42 carriesa projection 43 to provide the bearing proper. A lubricating systemsimilar to that of Figure 1 is mounted on projection 43. .A shaft H ismounted therein as in Figure 1 and a rotatable disk 45 is mountedthereon for rotation within the chamber 40. Otherwise, the departurefrom the design of Figure 1 is quite complete.

Both face-plate 4| and bearing-casing 42 are provided with opposed, andsubstantially rectangular in cross-section, annular projections orridges 41 and 48, respectively, near their outer peripheries. Inaddition to casings 4| and 42, a third plate or partition in the form ofa ring 4!, is used to enclose the cylindrical space 40. Thus, whencasings 4| and 42 are assembled with the intermediate ring 49 to dividethe chamber 44, two additional hollow spaces comprising the annularchambers 50 and BI are formed in the body of the apparatus. Face-plate4| is machined on its inner surface to provide a very narrowcommum'eating passage 52 between space 40 and 54. Similarly, bearingsection 42 is machined to provide a somewhat larger annular slotconnecting spaces 40 and 5|. The relatively narrow opening 52 near theouter periphery of plate 4| serves to connect space 50 with inlet 54 andconduit 55 and the similarly formed passageway or opening 53 connectsspace 5| to outlet 55 and conduit 51.

One feature should be noted. Clearance between the outer periphery ofdisk 45 and the inner wall of chamber 40 is kept at an absolutepractical minimum. This is in contrast with the clearance between diskl4 and the wall of the cylindrical chamber which has to be quitesubstantial. The peripheral edge of disk 45 is maintained in the desiredrelation to slots 52 and 53 by means of a ball bearing not shown heresince its function and location are identical to hearing l6 of Fig. 1.Lateral moving of the disk and shaft assembly in the direction of thehear ing section 2 is prevented by the atmospheric pressure on the shaftand pulley, this pressure is positive when the apparatus is in operationon account of the high vacuum prevailing in the cylindrical chamber. Ametallic, bellows diaphragm 58 is mounted between disk 45 and the innerface of bearing section 42. One face of the bellows is mounted on thebearing-casing by means of an outwardly projecting circular ridge 59which fits snugly into an annular groove 60 in the inner face of casing42. Theopposite face of bellows 58 carries a groove 6| made by suitablybending the material of the diaphragm. Mounted in groove BI is a bearingstrip 62 in the form of a ring made of a non-abrasive and low vaporpressure substance such as evacuated graphite from leaking into chamber40 and contaminating the gases being processed. Bearing strip 62 may bereplaced from time to time as ma be required. A conduit 65 communicateswith bearing-casing 42 at an oblique angle to the drive shaft andprovides a connection between the inner space within the bellowsdiaphragm and a suitable evacuating means, which not forming part of thepresent invention is not shown. Referring to Fig. 4, numeral 10designates a system to be evacuated, to which is connected a conduit 12which is, in turn, connected to the intake conduit 1 of my improvedmolecular pump. Numeral 14 designates a preliminary backing pump, theintake of which is connected to conduit 9 leading to the exhaust side ofmy improved molecular pump, This preliminary pump is capable ofproducing a relatively high vacuum of the order of .01 mm. andpreferably less. Numeral l2 designates the exhaust side of thepreliminar pump 14.

In operation the molecular centrifugal pump of Figure 1 is connected tothe molecular ce trifugal gas concentrator of Figure 3 by connecting theinlet 6 of Figure 1 to outlet 52 of Figure 3, condensation means or apreliminary vacuum pump or both are connected in series to the conduit 9of Figure 1, evacuating means are connected to conduit 65 of Figure 3,condensation means or vacuum pump or both are connected in series toconduit 51, the respective. disks of both apparatuses are made to rotateand the gaseous or vaporous mixture is allowed to pass from conduit 55into the annular chamber 50 and narrow slot 52 from which it effusesinto the chamber 40. The rate at which the mixture elfuses is controlledby its pressure in the annular chamber 50. This pressure can beregulated at the source of supply by any suitable means. The pressure ofthe efi'using mixture should be such that the mean free path of itsmolecules is greater than the distance between the inner side of theface plate 4| and the face of the disk opposite to it. In other wordsthere is a pressure it cannot exceed for the proper working of theprocess. This pressure is in the neighborhood of A000 of 1 millimeterabsolute. The molecules in the cylindrical chamber 40 on the averagestrike the moving disk more often than they collide among themselves,the molecules striking the moving disk are given a velocity having atangential component this action gives them a tendency to travel towardthe periphery, where they can escape through annular chamber 5|, opening56 and conduit 51, the are also urged to travel toward the centerthrough opening 52' due to the powerful action of the vacuum pump ofFigure 1. They cannot possibly escape through the narrow slot 52 (exceptfor an almost infinitesimal portion that might diffuse in that channel)for the pressure prevailing there is higher than in the cham- I ber 40.Obviously there will be a flow through both openings 56 and '52, but themolecules cannot possibly reach opening 52' without striking" againstthe rotating disk, the action of which tends to make them travel towardthe periphery and passage 53 and since the lighter molecules strike thedisc more often than the heavier ones, there is a greater probabilit ofthe lighter molecules reaching outlet 56 than there is for the heavierones which, on account of their greater molecular weight and lowervelocity, strike the rotating disc less oftenand consequently have alesser tendency to travel toward the periphery, It will be appreciatedthat by increasing the pressure of the gaseous mixture efiusing throughslot 52 and decreasing the capacity of the pump or condenser connectedat 51 the volume of flow toward 52 will be increased providing of coursethat the pump connected to it can take care of this increased flow. Onthe other hand an increase offlow toward the opening 56 can be producedby increasing the capacity of the'pump or condenser at 51. It will beapparent that an increase in flow in the direction of the opening 52"means a greater tendency of the molecules to travel in the directionopposite to the velocity having a tangential component given to themolecules by them striking against the moving disk.

B varying the pressure of the eifusing mixture and varying the. capacityof the pump or condenser at 51 the tendency of the molecules to traveleither toward the periphery and outlet 51 or in the opposite directiontoward the outlet 52 can thus be regulated and an optimum pressure orrate of feeding the gaseous mixture through slot 52, that pressure orrate of feeding which would pass the greatest percentage of'lightermolecules through conduit 5! can be ascertained experimentally. 'Whenthis optimum rate of feeding has been ascertained the system is readyfor continuous operation anda constant flow of a concentration oflighter molecules can becontinuously collected or condensed at theconduit 51 while a concentration of the heavier molecules can becollected or condensed at conduit 9 of the pump of Figure 1.

During the operation of the apparatus illustrated in Fig, 4 gases fromsystem 10 diffuse into the pump casing I through conduits 12 and 1. Thegases are forced into conduit 9 by the pumping action described above inconnection with Figs. 1 and 2. The pumped gases arethen taken into theintake side of pump 14 and are exhausted through conduit 12 by theaction of the pump 14. As a concentration of heavier molecules leavesthe outlet 52 of Figure 3 the enter the opening 6 of Figurel where thestrike against the rotating disk l8 which action imparts to them avelocity having a tangential component which produces a gradual movementof the molecules 7 towards the disks periphery; the general coursefollowed by the molecules is that of a spiral. The molecules at theperiphery accumulate in a crowded condition-hence at a higher pressurefrom where they can be collected or condensed by means connected toconduit 9.

A requisite condition for the proper working of both processes concernsthe machining of both I disks and their respective face plates: thenormal drawn from any point of the disk should also be a normal to apoint on the inner side of the disks respective face plate, except whenthis normal corresponds with the opening on the faceplate. A deviationfrom this rule apparently gives erratic and in some cases negativeresults.

Another requisite rule is the velocity of the respective disks. Itshould be as high as prac-v disks used. The maximum velocity at which adisk of the illustrated design can safel rotate depends of course on thematerial used on the diameter of the disk. Fora disk made of a goodnickel steel and of a 50 centimeter diameter a peripheral speed of 600meters a second is quite feasible. 'Disks' of substantially smallerdiameter are apparently not satisfactory on account of their relativelyshort radius which decreases the distance the molecules have to traveleither toward the periphery ortoward the center.

Referring tothe molecular centrifugal gas concentrator, I believe it tobe more efficient than any other known device such as super centrifugesor diffusion processes.

Referring to the molecular centrifugal pump I believe it to be a morerational rotary molecular pump than any other known rotary molecularpump. It has the advantage that its rotor or disk does not have to fitclosely against the wall of its casing thus allowing it to rotate at themaximum speed the centrifugal stress will stand, furthermore the designof its disk enabling it to withstand the maximum centrifugal stressesfor a given rim thickness cannot'be improved upon, and it is the firsttime a disk of such design is applied to molecular centrifugal machines.

The above descriptions are given by way of examples only and manymodifications can be made without departing from the scope of the invention.

I claim as my invention:

1. A molecular gas separating apparatus comprising a stationary housing,said housing ineluding a peripheral wall and cooperating front wall, thefront wall having an axially disposed outlet opening, a rotatable diskparallel to said front wall and extending into closely fittingrelationship with said peripheral wall, the thickness of said disc beingproportionate at all points to the centrifugal stresses to which saiddisc is subjected at said points when rotating at its operating speed,said disk and front wall definin a separating chamber of small constanttransverse dimension, the peripheral wall being provided with an inletslot adjacent the front wall and an outlet slot adjacent the face ofsaid disk, each of said slots extending substantially throughout thecircumference of the chamber, means for rotating said disk, means forsupplying a gase- 'ousmixture to said'inlet slot, means for with--drawing gas enriched in one of the constituents from said outlet slotand means for withdrawing gas enriched in another and differentconstituent from said axial outlet opening.

2. A molecular centrifugal process for exhausting a vacuum system to apressure substantially below /100 mm. Hg, comprising the preliminaryevacuation of the system to a pressure below 100 mm. Hg, the effusion ofthe residual gas moleculcsof the vacuum system into an innerlycylindrical enclosure. their free centrifugal travelling between twoopposing *walls ofsaid enclosure, their simultaneous back and forthcollisions with said walls, the average distance travelled by thesemolecules between two such collisions being constant and at least of thesame magnitude as the mean free path of thegases being treated andcontinuously withdrawing thus treated gases.

3. A molecular apparatus comprising a stationary housing, said housingincluding a cooperating wall having an axially disposed inlet opening, arotatable disc positioned in the housing so that the inside wall of thehousing and the surface of the disc are approximately parallel, bothsaid inside wall and the surface of the disc bein smooth and beingseparated from each other by a distance of less than about the mean freepath of the gases being pumped, means for rotating said disc and anoutlet means for gases, positioned peripherally with respect to thedisc.

4. A molecular pump comprising a stationary housing, said housingincluding a cooperating wall having an axially disposed inlet opening, arotatable disc decreasing in thickness in proportion to the centrifugalstresses to which it is subjected as the edge of the disc is approachedand positioned in the housing so that the inside wall of the housing andthe surface of the disc are approximately parallel, both said insidewall and the surface of the disc being smooth and being separated fromeach other by a. distance of less than about the mean free path of thegases being pumped, means for rotating said disc and an outlet means forcompressing gases positioned peripherally with respect to the disc.

5. A molecular centrifugal process of exhaustion which comprises thepreliminary evacuation of the system to a pressure below about .001 mm.

I Hg, introducing the residual gases in the system after the preliminaryexhaustion into a space between'two opposing approximately parallel andsmooth walls which walls are separated by a distance of less thanapproximately the mean free path of the residual gases in the system andwithdrawing gases after they have passed between the said opposingwalls.

6. A molecular gas separating apparatus comprising a stationary housingincluding a peripheral wall and a cooperating front wall, an axiallydisposed outlet opening in the front wall. a rotatable disc positionedwithin the housing so that it is approximately parallel with thecooperating front wall which disc is of such diameter that it extendsinto close fitting relationship with the peripheral wall and thethickness of the disc being proportionate at all points to thecentrifugal stresses to which said disc is subjected at said points whenrotating at its operating speed, said disc and front wall forming aseparating chamber of small and approximately constant transversedimension, the peripheral wall being provided with an inlet adjacent thefront wall for gases to be separated and an outlet for separated gasadjacent the face of the disc, means for rotating the disc, means forsupplying a gaseous mixture to the inlet for gases to be separated,means for withdrawing gases enriched in one of the components from theoutlet at the peripheral wall and means for withdrawing gas enriched inanother and different component from the said axial outlet opening.

ORBAN DENYS.

